Such a tensioning device is known from DE 10 2009 035923 A1, for instance. The tensioning piston is held in its retracted transport state by means of a transport locking device. In this transport state, a compression spring that is compressed under tension is located in a pressure reservoir and pushes against the tensioning piston. The transport locking device comprises a straight retainer pin, which engages into corresponding eyes on the housing of the chain tensioner and comes to rest on the tensioning piston with one shoulder, therefore preventing the tensioning piston from being deployed further. This design is a flange tensioner, which in this transport state is brought into its predetermined position on the engine block by means of corresponding fastening devices. After the fastening to the engine block, the retainer pin is pulled and the tensioning piston is deployed due to the spring force of the compression spring arranged in the pressure reservoir. A type of retainer clamp is seated in the front section of the housing, where said retainer clamp engages into a corresponding retainer profile on the exterior surface of the tensioning piston with its two opposing spring arms. The retainer clamp is designed in such manner that it fulfills several functions. The spring force pushes the tensioning piston out far enough against the push contact surface of a pivoting tensioning rail that a chain, which is in contact with this tensioning rail, is correspondingly tensioned. This is typically a timing chain of a timing chain drive for an internal combustion engine. The spring arms of the retainer clamp engage into one of the retainer grooves of the retainer profile, causing the retainer clamp now to come to rest on the tensioning piston and be able to move together with said tensioning piston. Because of correspondingly shaped pocket sections, the retainer clamp can move up and down relative to the housing over a defined working range. The housing has suitable protrusions that engage into these pocket sections of the retainer clamp, serving as upper or lower stops for the retainer clamp. The retainer clamp and the retainer profile are configured in such a way that while the tensioning piston can be deployed beyond the working range to accommodate wear related chain lengthening so that the retainer clamp can be brought into engagement with another retainer groove, it is no longer possible for the tensioning piston to be retracted beyond the working range. This results in an automatic adjustment of the working range depending on the wear state (lengthening) of the chain.
This known chain tensioner has the disadvantage that it can only be configured as a flange tensioner due to the transport locking device.
A tensioning device configured as a screw-in chain tensioner is described by WO 2009/024196 A1, for instance. This device is equipped with a reversibly, radially expandable locking sleeve that is attached on the front end of the housing. An arresting ring is arranged at the front end of the tensioning piston that is initially located outside of the locking sleeve. Activating the tensioning device exerts pressure on the tensioning piston, so that the arresting ring is inserted into the radially expandable locking sleeve, causing said locking sleeve to expand radially. The arresting ring's travel is afterward restricted to a predefined region within the locking sleeve. The arresting ring can then again travel from retainer groove to retainer groove on a retainer profile of the tensioning piston as a function of the chain lengthening; however this travel is only in one direction, with the ring locking in the other direction. This design has the disadvantage that it has no transport locking device and that the tensioning piston must be completely retracted before its first use, so that the arresting ring enters the locking sleeve. To do so, the tensioning piston must be retracted against the force of the compression spring, either during assembly or in the installed state. Due to the constrained space in the engine compartment, this activation of the adjustment function is frequently difficult.